Computer graphics, even when rendered in high quality, still appears flat when displayed on a flat monitor. Various approaches toward creating true stereoscopy have been proposed so that the objects that are simulated will look as though they are really in front of the observer [Okoshi, T. Three-Dimensional Imaging Techniques. Academic Press, New York 1976. ISBN 0-12-525250-1; L. Lipton, et. al., U.S. Pat. No. 4,523,226, Stereoscopic Television System, Jun. 11, 1985; and L. Lipton, and J. Halnon. Universal Electronic Stereoscopic Display. Stereoscopic Displays and Virtual Reality Systems III, Vol. 2653, pp. 219–223, SPIE, 1996], all of which are incorporated by reference herein]. These fall into various categories. The most common form of stereo display uses shuttered or passively polarized eyewear, in which the observer wears eyewear that blocks one of two displayed images from each eye. Examples include passively polarized glasses, and rapidly alternating shuttered glasses [L. Lipton, et al., U.S. Pat. No. 4,523,226, Stereoscopic Television System, Jun. 11, 1985, incorporated by reference herein]. These techniques have become workhorses for professional uses, such as molecular modeling and some subfields of CAD. But they have not found wide acceptance for three dimensional viewing among most students, educators, graphic designers, CAD users (such as engineers and architects), or consumers (such as computer games players). Studies have shown that observers tend to dislike wearing any invasive equipment over their eyes, or wearing anything that impairs their general ambient visual acuity [D. Drascic, J. Grodski. Defence Teleoperation and Stereoscopic Video. Proc SPIE Vol. 1915, Stereoscopic Displays and Applications IV, pages 58–69, San Jose, Calif. Feb. 1993, incorporated by reference herein]. This consideration has motivated a number of non-invasive approaches to stereoscopic display that do not require the observer to don special eyewear.
A graphical display is termed autostereoscopic when all of the work of stereo separation is done by the display [J. Eichenlaub, Lightweight Compact 2D/3D Autostereoscopic LCD Backlight for Games, Monitor, and Notebook Applications. Proc. SPIE Vol. 3295, p. 180–185, in Stereoscopic Displays and Virtual Reality Systems V, Mark T. Bolas; Scott S. Fisher; John O. Merritt; Eds. Apr. 1998, incorporated by reference herein], so that the observer need not wear special eyewear. A number of researchers have developed displays which present a different image to each eye, so long as the observer remains fixed at a particular location in space. Most of these are variations on the parallax barrier method, in which a fine vertical grating or lenticular lens array is placed in front of a display screen. If the observer's eyes remain fixed at a particular location in space, then one eye can see only the even display pixels through the grating or lens array, and the other eye can see only the odd display pixels. This set of techniques has two notable drawbacks: (i) the observer must remain in a fixed position, and (ii) each eye sees only half the horizontal screen resolution.
Holographic and pseudo-holographic displays output a partial light-field, computing many different views simultaneously. This has the potential to allow many observers to see the same object simultaneously, but of course it requires far greater computation than is required by two-view stereo for a single observer. Generally only a 3D lightfield is generated, reproducing only horizontal, not vertical parallax.
A display which creates a light field by holographic light-wave interference was constructed at MIT by [S. Benton. The Second Generation of the MIT Holographic Video System. In: J. Tsujiuchi, J. Hamasaki, and M. Wada, eds. +Proc. of the TAO First International Symposium on Three Dimensional Image Communication Technologies. Tokyo, 6–7 Dec. 1993. Telecommunications Advancement Organization of Japan, Tokyo, 1993, pp. S-3-1-1 to -6, incorporated by reference herein]. The result was of very low resolution, but it showed the eventual feasibility of such an approach. Discrete light-field displays created by [J. R. Moore, N. A. Dodgson, A. R. L. Travis and S. R. Lang. Time-Multiplexed Color Autostereoscopic Display. Proc. SPIE 2653, SPIE Symposium on Stereoscopic Displays and Applications VII, San Jose, Calif., Jan. 28–Feb. 2, 1996, pp. 10–19, incorporated by reference herein], and the recent work by Eichenlaub [J. Eichenlaub. Multiperspective Look-around Autostereoscopic Projection Display using an ICFLCD. Proc. SPIE Vol. 3639, p. 110–121, Stereoscopic Displays and Virtual Reality Systems VI, John O. Merritt; Mark T. Bolas; Scott S. Fisher; Eds., incorporated by reference herein], produce up to 24 discrete viewing zones, each with a different computed or pre-stored image. As each of the observer's eyes transitions from zone to zone, the image appears to jump to the next zone. A sense of depth due to stereo disparity is perceived by any observer whose two eyes are in two different zones.
Direct volumetric displays have been created by a number of researchers, such as [Elizabeth Downing et al. A Three-Color, Solid-State, Three-Dimensional Display. Science 273,5279 (Aug. 30, 1996), pp. 1185–118; R. Williams. Volumetric Three Dimensional Display Technology in D. McAllister (Ed.) Stereo Computer Graphics and other True 3D Technologies, 1993; and G. J. Woodgate, D. Ezra, et.al. Observer-tracking Autostereoscopic 3D display systems. Proc. SPIE Vol. 3012, p. 187–198, Stereoscopic Displays and Virtual Reality Systems IV, Scott S. Fisher; John O. Merritt; Mark T. Bolas; Eds., all of which are incorporated by reference herein]. One commercial example of such a display is Actuality Systems. A volumetric display does not create a true lightfield, since volume elements do not block each other. The effect is of a volumetric collection of glowing points of light, visible from any point of view as a glowing ghostlike image.
Autostereoscopic displays that adjust in a coarse way as the observer moves have been demonstrated by [G. J. Woodgate, D. Ezra, et. al. Observer-tracking Autostereoscopic 3D display systems. Proc. SPIE Vol. 3012, p.187–198, Stereoscopic Displays and Virtual Reality Systems IV, Scott S. Fisher; John O. Merritt; Mark T. Bolas; Eds., incorporated by reference herein]. The Dresden display [A. Schwerdtner and H. Heidrich. Dresden 3D display (D4D) . SPIE Vol. 3295, p. 203–210, Stereoscopic Displays and Virtual Reality Systems V, Mark T. Bolas; Scott S. Fisher; John O. Merritt; Eds., incorporated by reference herein] mechanically moves a parallax barrier side-to-side and slightly forward/back, in response to the observer's position. Because of the mechanical nature of this adjustment, there is significant “settling time” (and therefore latency) between the time the observer moves and the time the screen has adjusted to follow. In both of these displays, accuracy is limited by the need to adjust some component at sub-pixel sizes.
The goals of the present invention have been to present a single observer with an artifact-free autostereoscopic view of simulated or remotely transmitted three dimensional scenes. The observer should be able to move or rotate their head freely in three dimensions, while always perceiving proper stereo separation. The subjective experience should simply be that the monitor is displaying a three dimensional object. In order to be of practical benefit, the present invention provides a solution that could be widely adopted without great expense and that would not suffer from the factor-of-two loss of horizontal resolution which is endemic to parallax barrier systems.
These goals imposed certain design constraints. The user responsive adjustment could not contain mechanically moving parts, since that would introduce unacceptable latency. The mechanism could not rely on very high cost components and needed to be able to migrate to a flat screen technology.
The significance of the present invention is in that it enables a graphic display to assume many of the properties of a true three dimensional object. An unencumbered observer can walk up to an object and look at it from an arbitrary distance and angle, and the object will remain in a consistent spatial position. For many practical purposes, the graphic display subjectively becomes a three dimensional object. When combined with haptic response, this object could be manipulated in many of the ways that a real object can. Ubiquitous non-invasive stereo displays hold the promise of fundamentally changing the graphical user interface, allowing CAD program designers, creators of educational materials, and authors of Web interfaces (to cite only some application domains) to create interfaces which allow users to interact within a true three dimensional space.